Wire and other elongated members can be coated by passing them through a fluidized powder. If the wire is heated the powder melts on contact and forms a coating. If the powder is charged and the wire is grounded, the powder clings to the wire until the wire passes through an oven where the powder melts and coats the wire.
The thickness or build of the coating on one side of the wire may be more or less than the thickness on the rest of the wire. This may be due to the uneven movement of the powder in the bed, or in an electrostatic bed to a non-uniform electrostatic field around the wire due to the presence of interfering objects. Often the cause of the non-uniformity of the coating cannot be readily ascertained.
In any event, a wire which is not coated uniformly may be entirely unusable since a too thin coating may not provide adequate insulation and a too thick coating may mean that the wire will not fit, in addition to wasting powder.